Manufacture of α-naphthol

ABSTRACT

Process for the manufacture of α-naphthol by hydrolyzing α-naphthyl esters of aliphatic carboxylic acids in a distillation column by means of steam in counter-current at a particular temperature, and in a certain ratio, in the presence of naphtholsulfonic acids and/or sulfonic acids of naphthyl esters. The α-naphthol obtainable by the process of the invention is a valuable starting material for the manufacture of dyes, drugs and insecticides, e.g. α-naphthyl N-methylcarbamate.

The present invention relates to a new process for the manufacture ofα-naphthol by hydrolyzing α-naphthyl esters of aliphatic carboxylicacids in a distillation column by means of steam in counter-current at aparticular temperature, and in a certain ratio, in the presence ofnaphtholsulfonic acids and/or sulfonic acids of naphthyl esters.

Ullmanns Encyklopadie der technischen Chemie, volume 18, pages 72 and 73discloses that esters can be hydrolyzed catalytically to the alcohol andthe acid by means of water in the presence of an acid or base. In thecase of esters of alkalecarboxylic acids, e.g. of fatty acids, thehydrolysis to the acid is as a rule carried out under pressure in thepresence of emulsifiers. Optimal hydrolysis is achieved by heating theester for five hours in a mixture of formic acid and methanesulfonicacid.

As shown by the Comparative Example, the hydrolysis of α-naphthylesters, especially α-naphthyl acetate, is a very slow reaction. To carryout the hydrolysis, the ester must be thoroughly mixed for several hourswith water at 200° C. under a pressure of up to 20 bars. However, whencarried out in this way the hydrolysis only proceeds to an equilibriumat which, when using economically acceptable amounts of water, there arestill about 2 percent by weight of ester present. Under the severereaction conditions employed, substantial corrosion of the materials ofthe vessels occurs, so that expensive, highly resistant materials ofconstruction, e.g. titanium or tantalum, must be used. The reactiongives a dilute acetic acid which, before it can be re-used, must bere-concentrated in an expensive process step.

German Published Patent Application No. B 64 09.12 0, 11 disclosesrunning a mixture of water and carboxylic acid ester into the upper partof a distillation column, introducing steam into the column at a lowerpoint, and heating the column so that the acid formed distils off. Thereaction is carried out in the presence of hydrolysis catalysts; thecatalysts named are mineral acids, e.g. sulfuric acid, silica gel andsolid synthetic resin ion exchangers which are used for waterpurification, e.g. a phenol/formaldehyde/sodium sulfite condensationproduct. Only monohydric or polyhydric aliphatic alcohols are mentionedas the alcohol constituent of the ester. An essential feature of theprocess is that a large excess of water is used; a part of the water isintroduced into the column as a mixture with the ester, and accordinglyenters in co-current from above. Even this water, introduced inco-current with the ester, is advantageously used in excess over thelatter. The column temperature is set to a value where some waterdistils off continuously. The product taken off at the bottom is also amixture of water and end product. As is shown in Example 3, thedistillate still contains unconverted ester, and must bere-fractionated.

We have found that α-naphthol is obtained in an advantageous manner byhydrolyzing carboxylic acid esters with steam in a distillation columnin the presence of an acid, if an α-naphthyl ester of an aliphaticcarboxylic acid, of the formula ##STR1## where R is hydrogen or analiphatic radical, and a naphtholsulfonic acid and/or sulfonic acid of anaphthyl ester is passed downward through the column whilst steam ispassed upward in counter-current, and the reaction is carried out atfrom 100° to 170° C. using a ratio of from 0.9 to 1.5 moles of water permole of α-naphthyl ester I.

Where α-naphthyl acetate is used, the reaction can be represented by thefollowing equation: ##STR2##

Compared to the prior art, the process of the invention gives α-naphtholmore simply and more economically, and in better yield and greaterpurity. The process is also relatively more suitable for continuousoperation and/or industrial operation. Compared to the German PatentApplication cited above, the process of the invention gives a purer endproduct directly, with no substantial proportion of water or ester inthe distillate or in the bottom product. No water is added to thestarting material. Altogether, a substantial excess of water, relativeto the ester, is not used; as a rule, virtually stoichiometric amountsare employed. The total amount of the water used is passed upwardsthrough the column, in countercurrent. As a rule, the column is notheated. Neither the starting material nor the catalyst according to theinvention are apparent from the cited German Patent Application.

Preferred starting materials I are those where R is hydrogen or alkyl of1 to 7 carbon atoms, especially of 1 to 4 carbon atoms. The aboveradicals may be substituted by groups which are inert under the reactionconditions, e.g. alkyl or alkoxy each of 1 to 4 carbon atoms. Examplesof suitable esters I are the α-naphthyl esters of formic acid, aceticacid, propionic acid, butyric acid, isobutyric acid, tetracosanoic acid,hexacosanoic acid, myristic acid, arachidic acid, behenic acid, caproicacid, enanthic acid, pelargonic acid, capric acid,3,5,5-trimethylhexanoic acid, undecanoic acid, lauric acid, palmiticacid, stearic acid, 2-ethylhexanecarboxylic acid, α-ethylbutyric acid,2-methylbutanoic acid, trimethylacetic acid, valeric acid, isovalericacid, isocaproic acid, nonanoic acid, tridecanoic acid, pentadecanoicacid and heptadecanoic acid; formic acid, acetic acid and propionic acidare preferred.

The reaction is carried out at from 100° to 170° C., preferably from120° to 165° C., advantageously from 130° to 150° C., especially from140° to 150° C., under atmospheric or superatmospheric pressure,batchwise or preferably, continuously. At lower temperatures,low-boiling constituents, e.g. acetic acid, are not substantiallyremoved from the naphthol. For example, at temperatures near the boilingpoint of the carboxylic acid, the latter no longer distils off at thetop of the column; it is true that the naphthyl acetate is hydrolyzed,but the second effect desired, i.e. the recovery of a concentratedcarboxylic acid, e.g. acetic acid, is no longer achieved. On the otherhand, at even higher temperatures (above 170° C.) a side-reaction ofnaphthol, namely the formation of condensed products of higher molecularweight under the action of the sulfonic acid, becomes more noticeable.The desired reaction temperature can within limits be controlled by thetemperature of the individual reactants entering the column, e.g. steamand the naphthyl ester I. Additional heating or cooling can be effectedthrough the walls of the column. Finally, in the case of substantialcolumn diameters, trays comprising cooling coils or cooling pockets canbe introduced. Preferably, the ester I is brought to from 60° to 180°C., advantageously from 70° to 150° C., preferably from 80° to 130° C.before entering the column.

The residence time is generally from 10 to 90, advantageously from 20 to40, preferably from 20 to 36, minutes. The hydrolysis is carried outusing a ratio of from 0.9 to 1.5, advantgeously from 1 to 1.4,preferably from 1.1 to 1.3, moles of water, in the form of steam, permole of α-naphthyl ester I. As a rule, a slight excess of water relativeto ester I, over the stoichiometric amount is used. The steam may or maynot be superheated and is advantageously supplied at from 100° to 170°C., preferably from 130° to 155° C., and at a pressure of from 0.5 to 3,preferably from 0.98 to 2 bars.

Naphtholsulfonic acids and/or sulfonic acids of naphthyl esters areused, advantageously those of the formula ##STR3## where the individualradicals R² are identical or different and one R² is a sulfonic acidgroup whilst the remaining R² may each be hydrogen, a sulfonic acidgroup or--OR³, R³ is hydrogen or ##STR4## and R⁴ is hydrogen, acycloaliphatic radical, advantageously cyclohexyl or cyclopentyl, anaraliphatic radical, advantageously benzyl, an aromatic radical,advantageously phenyl or naphthyl, and especially an aliphatic radical,advantageously alkyl of 1 to 7 carbon atoms. The above radicals may besubstituted by groups which are inert under the reaction conditions, forexample alkyl or alkoxy each of 1 to 4 carbon atoms. Where there is morethan one radical R³ and/or R⁴ in the compound II, the individualradicals R³ or R⁴ may be identical or different. Mixtures of compoundsII may also be used. Furthermore, in place of the sulfonic acids II,compounds which form such sulfonic acids under the reaction conditions,e.g. α-naphthol and chlorosulfonic acid, may be employed. In general,the amounts used are from 0.002 to 0.02, preferably from 0.005 to 0.01,mole of sulfonic acid per mole of starting material I. Advantageoussulfonic acids are disulfonic acids and, more particularly, monosulfonicacids of dihydroxynaphthalenes, especially of 1,5-, 1,6-, 1,7-, 1,8- and2,3-dihydroxynaphthalene; trisulfonic acids, more advantageouslydisulfonic acids and especially monosulfonic acids of β-naphthol andespecially of α-naphthol; and corresponding esters of the abovehydroxynaphthalenes, preferably esters where R⁴ is methyl, ethyl,n-propyl, isopropyl, n-butyl, isobutyl, sec.-butyl, tert.-butyl,cyclohexyl, cyclopentyl, benzyl or phenyl, or is hydrogen; amongst theesters, the sequence of increasing preference is diester-disulfonicacids, monoester-monohydroxydisulfonic acids,monoester-monohydroxymonosulfonic acids, diester-monosulfonic acids,β-naphthyl ester-trisulfonic acids, α-naphthyl ester-trisulfonic acids,β-naphthyl ester-disulfonic acids, α-naphthyl ester-disulfonic acids,β-naphthyl ester-monosulfonic acids, and α-naphthyl ester-monosulfonicacids. The use of the following is particularly advantageous:1,8-dihydroxynaphthalene-4-sulfonic acid,2,3-dihydroxynaphthalene-6-sulfonic acid,2,5-dihydroxynaphthalene-7-sulfonic acid,2,8-dihydroxynaphthalene-6-sulfonic acid,1,8-dihydroxynaphthalene-3,6-disulfonic acid,1-naphthol-3,6,8-trisulfonic acid, 2-naphthol-3,6,8-trisulfonic acid,1-naphthol-3,6-disulfonic acid, 1-naphthol-3,8-disulfonic acid,2-naphthol-1-sulfonic acid, 2-naphthol-4-sulfonic acid,2-naphthol-6-sulfonic acid, 2-naphthol-7-sulfonic acid,2-naphthol-8-sulfonic acid, 1-naphthol-3-sulfonic acid,1-naphthol-4-sulfonic acid, 1-naphthol-5-sulfonic acid,1-naphthol-8-sulfonic acid as well as the above esters, containingpreferred radicals R⁴, of these naphthols, e.g. the di-acetate ester ormono-acetate ester. Particularly preferred compounds are the formicacid, acetic acid and propionic acid esters of α-naphthol-3-sulfonicacid, α-naphthol-4-sulfonic acid, α-naphthol-5-sulfonic acid andα-naphthol-8-sulfonic acid, as well as free α-naphthol-3-sulfonic acid,α-naphthol-4-sulfonic acid, α-naphthol-5-sulfonic acid andα-naphthol-8-sulfonic acid, especially α-naphthol-4-sulfonic acid andα-naphthyl acetate-4-sulfonic acid, and mixtures of these.

The distillation may be carried out in any distillation column,advantageously in a rectifying column, e.g. a sieve tray column,Oldershaw column, thin layer evaporator, falling curtain distillationapparatus, glass tray column, bubble-cap tray column, valve tray column,packed column or column with rotating inserts. It is advantageous to usetray columns which can be operated continuously at a rate of from 0.1 to0.4 part by volume/hour of ester entering the column per part by volumeof the total capacity of the column. In the case of bubble-cap traycolumns, a weir height of from 10 to 300 mm is preferred, whilst in thecase of ball valve tray columns and sieve tray columns hole diameters offrom 5 to 15 mm, ball diameters of from 8 to 30 mm and tray spacings offrom 300 to 800 mm are preferred. In continuous operation, the steam canbe introduced into the distillation boiler or, advantageously, betweenthe lowest and next-but-lowest tray of the column. The ester I may beintroduced together with the catalyst or separately therefrom; theseparate feed points can be anywhere in the upper part of the column,but are preferably at the column top. It is advantageous to use a typeof column which is insensitive to the low vapor throughput resultingfrom the fact that the steam is introduced in virtually stoichiometricamount. Furthermore, it should be possible to select the residence timevery precisely. This in itself is a reason for particularly preferring abubble-cap tray column.

The hydrolysis may be carried out as follows: a mixture of the catalystand the ester I is passed downward, and steam is passed upward, througha column, in the above amounts, and the hydrolysis is carried out incounter-current, at the reaction temperature. At the same time, thecarboxylic acid formed is continuously removed as distillate and theα-naphthol is continuously removed from the bottom.

The α-naphthol obtainable by the process of the invention is a valuablestarting material for the manufacture of dyes, drugs and insecticides,e.g. α-naphthyl N-methylcarbamate. It may also be used as a couplingcomponent for azo dyes, as a starting material for indigoid dyes, andfor the synthesis of 4-chloro-1-naphthol, 1-naphthol-2-carboxylic acidand naphthyl salicylate. Regarding the uses of the material, referencemay be made to Ullmanns Encyklopadie der technischen Chemie, volume 12,pages 603-604.

In the Examples which follow, parts are by weight.

EXAMPLE 1

Per hour, 4,000 parts of α-naphthyl acetate and 35 parts of1-naphthol-4-sulfonic acid are introduced, in the form of a melt, at140° C., at the top end (above the top tray) of a bubble-cap tray columnwith 18 trays, operated at 140° C. (reaction temperture). At the bottomend (below the bottom tray), 390 parts of water per hour are introducedin the form of superheated steam at 150° C. under 1.3 bars. Theresidence time is 35 minutes. At the top of the column is a condenser,from which 1,270 parts per hour of acetic acid are taken off. 2,160parts/hour of α-naphthol, of boiling point 130° C./13 mbar, are takenoff the bottom of the column. The yield is 98.5% of theory.

EXAMPLE 2

Per hour, 3,700 parts of α-naphthyl formate and 35 parts of1-α-naphthyl-acetate-4-sulfonic acid are introduced, in the form of amelt, at 140° C., at the top end (above the top tray) of a bubble-captray column with 18 trays, operated at 130° C. (reaction temperature).At the bottom end (below the bottom tray), 390 parts of water per hourare introduced in the form of super-heated steam at 150° C. under 1.3bars. The residence time is 35 minutes. At the top of the column is acondenser, from which 1,020 parts per hour of formic acid are taken off.3,060 parts/hour of α-naphthol, of boiling point 130° C./13 mbar, aretaken off the bottom of the column. The yield is 96% of theory.

EXAMPLE 3

Per hour, 4,500 parts of α-naphthyl butyrate and 50 parts of1,8-dihydroxy-naphthalene-3,6-disulfonic acid are introduced, in theform of a melt, at 165° C., at the top end (above the top tray) of abubble-cap tray column with 18 trays, operated at 169° C. (reactiontemperature). At the bottom end (below the bottom tray), 390 parts ofwater per hour are introduced in the form of superheated steam at 160°C. under 1.3 bars. The residence time is 35 minutes. At the top of thecolumn is a condenser, from which 1,860 parts per hour of butyric acidare taken off. 2,760 parts/hour of α-naphthol, of boiling point 130°C./13 mbar, are taken off the bottom of the column. The yield is 92% oftheory.

EXAMPLE 4

Per hour, 4,100 parts of α-naphthyl propionate and 60 parts of1-naphthol-8-sulfonic acid are introduced, in the form of a melt, at150° C., at the top end (above the top tray) of a bubble-cap tray columnwith 18 trays, operated at 150° C. (reaction temperature). At the bottomend (below the bottom tray), 390 parts of water per hour are introducedin the form of superheated steam at 150° C. under 1.3 bars. Theresidence time is 35 minutes. At the top of the column is a condenser,from which 1,210 parts per hour of propionic acid are taken off. 2,760parts/hour of naphthol, of boiling point 130° C./13 mbar, are taken offthe bottom of the column. The yield is 95% of theory.

EXAMPLE 5 (COMPARATIVE EXAMPLE)

201 parts of α-naphthyl acetate and 45 parts of water are introducedinto a stirred autoclave, the mixture is heated to 200° C., whilststirring, resulting in an autogenous pressure of 15 bars. After 75minutes at 200° C., the emulsion formed changes to a clear solution.After 6 hours at 200° C., the mixture is distilled. 134.5 parts ofα-naphthol (86.5% of theory) of boiling point 130° C./13 mbar, 3 partsof naphthyl acetate and 9.5 parts of residue are obtained.

We claim:
 1. A process for the manufacture of α-naphthol by hydrolyzinga carboxylic acid ester with steam in a distillation column in thepresence of an acid, wherein an α-naphthyl ester of an aliphaticcarboxylic acid, of the formula ##STR5## where R is hydrogen or an alkylof 1 to 7 carbon atoms, which may be substituted by alkyl or alkoxy eachof 1 to 4 carbon atoms, and a naphtholsulfonic acid or sulfonic acid ofa naphthyl ester are passed downward through the column whilst steam ispassed upward in counter-current, and the reaction is carried out atfrom 100° to 170° C. using from 0.9 to 1.5 moles of water per mole ofα-naphthyl ester I.
 2. A process as claimed in claim 1, wherein thereaction is carried out at from 120° to 165° C.
 3. A process as claimedin claim 1, wherein the reaction is carried out at from 130° to 150° C.4. A process as claimed in claim 1, wherein the reaction is carried outat from 140° to 150° C.
 5. A process as claimed in claim 1, wherein theester I is brought to a temperature of from 60° to 180° C. before itenters the column.
 6. A process as claimed in claim 1, wherein thereaction is carried out with a residence time of from 10 to 90 minutes.7. A process as claimed in claim 1, wherein the reaction is carried outwith from 1 to 1.4 moles of water, in the form of steam, per mole ofα-naphthyl ester I.
 8. A process as claimed in claim 1, wherein thereaction is carried out with from 1.1 to 1.3 moles of water, in the formof steam, per mole of α-naphthyl ester.
 9. A process as claimed in claim1, wherein the reaction is carried out using steam supplied at from 100°to 170° C.
 10. A process as claimed in claim 1, wherein the reaction iscarried out under a pressure of from 0.5 to 3 bars.
 11. A process asclaimed in claim 1, wherein the reaction is carried out using from 0.002to 0.02 mole of a naphtholsulfonic acid and/or sulfonic acid of anaphthyl ester per mole of starting material I.